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Astrophysics

Title:On the migration of protoplanets embedded in circumbinary disks

Abstract: We present the results of hydrodynamical simulations of low mass protoplanets
embedded in circumbinary accretion disks. The aim is to examine the migration
and long term orbital evolution of the protoplanets, in order to establish the
stability properties of planets that form in circumbinary disks. Simulations
were performed using a grid--based hydrodynamics code. First we present a set
of calculations that study how a binary interacts with a circumbinary disk. We
evolve the system for 10^5 binary orbits, which is the time needed for the
system to reach a quasi-equilibrium state. From this time onward the apsidal
lines of the disk and the binary are aligned, and the binary eccentricity
remains essentially unchanged with a value of e_b ~ 0.08. Once this stationary
state is obtained, we embed a low mass protoplanet in the disk and let it
evolve under the action of the binary and disk forces. We consider protoplanets
with masses of 5, 10 and 20 Earth masses. In each case, we find that inward
migration of the protoplanet is stopped at the edge of the tidally truncated
cavity formed by the binary. This effect is due to positve corotation torques,
which can counterbalance the net negative Lindblad torques in disk regions
where the surface density profile has a sufficiently large positive gradient.
Halting of migration occurs in a region of long-term stability, suggesting that
low mass circumbinary planets may be common, and that gas giant circumbinary
planets should be able to form in circumbinary disks.